Gender reveal party

So my anatomy scan isn't scheduled until almost 22 weeks so I am going to pay to find out earlier at another place. For the ladies who have had a gender reveal party how did you plan it? Do you just tell your guests that the date but it's pending whether or not the baby cooperates? What did you do if you couldn't figure out on the day you thought you could? Or did you just plan it for way later so you would know for sure?